Radiation alarm or the like



Sept. 25, 1962 M. H. SHAMOS 3,056,123

1 RADIATION ALARM OR THE LIKE Filed July 29, 1958 2 Sheets-Sheet 1 I I IQ I I M I L E \f I 3: 2 g I' Y o i /A *28 INVENTOR- QL-EEE MORRISH.SHAMOS ATTOR N EYS.

Sept. 25, 1962 M. H. SHAMOS 3,056,123

RADIATION ALARM OR THE LIKE Filed July 29, 1958 2 Sheets-Sheet 2lllllllw INV/Vf0R.. MORRIS H. SHAMOS ii/.4, 211M KM ATTORNEYS.

nited Stats rt 3,056,123 RADIATION AL OR THE LIKE Morris H. Shamos,Riverdale, N.Y., assignor to Tung-Sol Electric Inc., a corporation ofDelaware Filed July 29, 1958, Ser. No. 751,715 Claims. (Cl. 340-237)This invention relates to alarm devices and has particular reference toan alarm system which will sound a warning or produce a visualindication when gamma ray radiation level exceeds a predeterminedtolerance level.

The large increase in the use of radioactive materials during the pastfew years, coupled with the threat of radiation hazards resulting fromatomic warfare make it desirable to have a simple, automatic radiationalarm which will give a signal when the radiation level exceeds apredetermined value. Since such devices should be on duty twenty-fourhours a day, it is advisable to use a simple dependable arrangementwhich does not require a continuous supply of electrical energy in thestandby condition.

The present invention, while primarily directed to the detection ofgamma and X-ray radiation, can also be arranged to act as a smoke alarmand as such can be used in the home or in any building where there isdanger from fire.

Radiation alarms used at present generally consist of ion chambers orGeiger counters coupled to appropriate amplifier circuits to operatepreset relays and alarm sys terns. In any of these devices hot cathodetubes must be used which require a continuous supply of heater orfilament current in the standby condition. The level for which thesealarms are set is usually the accepted tolerance level, which is 6.25milliroentgens per hour.

The alarm described herein is an improvement on the alarm described inUs. Patent No. 2,817,768, issued December 24, 1957 to Morris H. Shamos.

One of the objects of this invention is to provide an improved radiationalarm which avoids one or more of the disadvantages and limitations ofprior art arrangements.

Another object of the invention is to provide a radiation alarm whichconsumes almost no electrical energy in the standby condition.

Another object of the invention is to increase the sensitivity ofradiation alarms.

. Another object of the invention is to provide a radiation alarm whichmay be used to detect neutrons or beta radiation as well as gammaradiation.

Another object of the invention is to provide an alarm which detects thepresence of smoke.

Briefly the invention comprises two constant current devices connectedin series across a source of energy and an electrostatic switchconnected in series with a high resistor across one of the devices withits switch arm normally positioned between two electrodes, one of whichis connected to the junction between the devices and the other of whichis maintained at a substantially fixed potential. Actuation of theswitch in response to the electric field existing between the electrodescauses energization of an alarm device. One of the constant currentdevices may be an ionization chamber having a resistance responsive topenetrating radiation and the other of the constant current devices maybe sensitive to the presence of smoke and dust. In one embodiment of theinvention the last mentioned electrode of the elec trostatic switchserves as an electrical contact and is connected to the firing electrodeof a gaseous discharge device, the discharge device, when triggered,causing energization of the alarm. In another embodiment of theinvention a separate contact is provided for engagement by the movablearm of the electrostatic switch, the switch arm in this embodimentcompleting an energizing circuit for the alarm when the switch isactuated.

For a better understanding of the present invention, together with otherand further objects thereof, reference is made to the followingdescription taken in connection with the accompanying drawings.

FIG. 1 is a schematic diagram of connections showing one arrangement ofthe alarm circuit.

FIG. 2 is a schematic diagram of connections showing an alternatearrangement using a photoelectric cell and a self luminous source.

FIG. 3 is a graph showing the characteristics of the two constantcurrent devices.

FIG. 4 is a schematic diagram of connections showing another alternatearrangement using two photoelectric cells.

FIG. 5 is a schematic diagram of connections using an electrostaticswitch or relay without a vacuum or gaseous discharge device.

Referring now to FIG. 1 the alarm comprises an ionization chamber 10connected in series with a constant current device 11 and a source ofpotential T2. The ionization chamber id is a constant current devicewithin a well defined range of applied voltages. The constant currentdevice 11 includes two electrodes mounted with lead-in conductors whichmay be sealed to a partial glass envelope. The space between theelectrodes, however, must be open to the atmosphere in order to detectthe presence of smoke. Any other type of insulation mounting can be usedfor the two electrodes as long as they are securely mounted and open tothe atmosphere. The space between the electrodes is subject to constantionization by some radioactive material such as radium and this materialmay be conveniently supported on one of the electrodes as shown in thefigure. While the circuit will function without any means of ionizationin envelope 10, it has been found advisable to include some radioactivematerial in this device also.

A discharge circuit is also connected across the source of potential 12and includes a three electrode gaseous discharge device 13 containing acathode, an anode, and a firing electrode. The discharge device 13 isconnected in series with a high resistor 14, and an alarm 15. Acapacitor 16 is connected between the anode and the negative terminal ofthe potential source 12 and aids in the dis charge of the device 13 byfurnishing a quantity of electricity which flows through the dischargedevice 13 and the alarm 15 whenever the firing electrode renders thedevice conductive. The firing electrode is connected to the negativeterminal of source 12 by a high resistor 17.

An electrostatic switch 18 is employed in this circuit to make thedevice more sensitive and more reliable. The switch is enclosed in anair-tight envelope and is a single pole, single throw switch having amovable element 29, which may be a metalized quartz fiber, and twoelectrodes 22 and 23, the latter also serving as the switch contact. Theswitch is normally open, as shown in the figures, and under normalconditions of no penetrating radiation, there is practically no forceexerted on the movable member to be actuated. Both electrodes 22 and 23are at about zero potential and there is no electrostatic field betweenthem. When this switch is operated, the movable member 29 is moved tothe position indicated by the dotted line and makes contact with aconductor connected to the firin electrode of the discharge device 13.

Both constant current devices 10 and 11 possess a constant currentfeature Within their range which extends from about 15 volts to about200 volts, the upper limit depending upon the spacing and area of theelectrodes. At values between 0 and 15 volts the devices act as normalresistors, and above 200 volts secondary electronic processes cause thecurrent to increase sharply. When no ambient ionizing radiation is beingreceived the ionization chamber passes only a small current and thiscurrent is below the normal constant current of the device 11, whichbecause of its constant source of ionization can conduct a largercurrent. It the voltage of the potential source is 200 volts, thensubstantially all of this voltage under these conditions is across theionization chamber 10 and only a few volts, less than the criticalvolts, is applied across the constant current device 11.

The division of voltages across devices 10 and 11 may be betterexplained by reference to the graph shown in FIG. 3. Here thecharacteristic curve of the ionization chamber 10 is shown at A. Thechamber passes a small current I because of the small amount ofradioactive material deposited within its envelope. The characteristiccurve B for the constant current device 11 is plotted in a reversedirection. That device is adapted to pass about three times as muchcurrent (1 because it contains considerably more radioactive material.When no ambient ionizing radiation is being received, the voltages arerepresented by the intersection 2t; of curves A and B applying about 6volts across device 11 and about 200 less 6 or 194 volts across chamber10.

When penetrating radiation is incident upon the ionization chamber 19,causing it to be more conductive than device 11 (curve D), the potentialditIerences across each component shift; the drop across chamber 10becomes lower while the drop across device 11 becomes higher. Thisaction changes the potential of contact 22 abruptly, raising it to avalue which may be as high as 180 volts (with 200 volts supplied bysource 12). This condition is represented in the graph in FIG. 3 byintersection 30. Since contact 23 is at zero potential an electrostaticfield is set up between electrodes 22 and 23 and since member is at 200volts, it is attracted toward the zero potential electrode 23 Whilebeing repulsed by the positive potential electrode 22. When member 20moves to its actuated position as shown by the dotted line in thefigures, the potential of the firing electrode in triode 13 is raisedand the triode conducts. Capacitor 16 now discharges through the alarm15, operating it and giving notification that the penetrating radiationapplied to chamber 10 is above a predetermined value.

Curve C represents the characteristic of chamber 10 when an intermediateamount of radiation is being received by the chamber (less than thepredetermined value).

FIG. 1 shows device 11 open to the atmosphere because of the cut-awayportion 31 of its envelope. Small changes in atmospheric pressure havevery little efiect on discharge device 11 and this device generallyoperates well at this pressure. Since the electrodes and the spacebetween them are open to the atmosphere, smoke particles which might bethe result of a fire can enter the space between the electrodes andreduce the current between the electrodes either by masking the alpharays and thereby reducing ionization or else by causing recombination ofthe ionized gas molecules. In either case the current through device 11is lowered causing a large change of voltage similar to the operationdescribed above and the alarm is again operated.

The circuit shown in FIG. 2 is the same as FIG. 1 except that aphotoelectric cell 24 is used as a circuit component instead of theconstant current device 11. The photoelectric cell 24 is enclosed in alight tight shield 25 having access to the atmosphere through a seriesof bafile plates 26. A small quantity of luminescent material 27 ispositioned adjacent to the cell 24 and causes a constant current to flowthrough the cell. Under such conditions, photoelectric cells possessconstant current characteristics similar to device 11. The operation ofthis circuit is similar to the operation of the circuit shown in FIG. 1.When smoke passes through the shield baflle plates it cuts off the lightfrom material 27 and causes an abrupt shift in voltage across chamber 10and cell 24.

The circuit shown in FIG. 4 is the same as that shown in FIG. 2 exceptthat a second photoelectric cell 32 is substituted for the ionizationchamber 10. This second cell 32 i mounted in a light tight case 33 whichmay be made of thin aluminum and which is also gas tight.

A scintillation crystal 34 is mounted within the case 33 and lights upwhenever bombarded by ionizing radiation. A small portion ofradio-active material 35 such as a radium salt, is placed adjacent tothe crystal to provide the background current necessary to produce thecurrent indicated by curve A in FIG. 3. The operation of the circuit isas described above.

For certain installations where a more rugged form of electrostaticswitch may be used, the gaseous triode 13 may be omitted and the circuitshown in FIG. 5 be employed. This circuit includes two constant currentdevices 4G and 41 in series connection, one of the devices beingcontrolled by bombarding penetrating radiation. Either one of thedevices, It 11, 24, or 32, a illustrated in FIGS. 1, 2 and 4, may beused in these positions. Source of potential 12 is connected across bothof the components 49 and 41, and the positive terminal is connected inseries with a high resistor 21 to the movable blade 2% of the switch18A. This form of switch includes tWo electrodes 22 and 42 which areused exclusively for setting up an electrostatic field. Switch 18A alsoincludes a contact 23, as before, but in this circuit it is connecteddirectly to the alarm 15. The storage capacitor 16 is connected betweenthe negative terminal of the source 12 and the movable switch blade 20.Electrode 42 is connected to the negative terminal of source 12 througha protective resistor 4-3.

The operation of this circuit (FIG. 5) is similar to the circuitsdescribed above except that when the voltage shifts and the switch isoperated, the current from the charged capacitor 16 flows through theblade 20, through contact 23, and through the alarm 15, back to theother side of the capacitor 16. Since all the above described circuitsare not designed to be operated at fast repetition rates, the capacitormay be charged slowly with resistor 14 in FIGS. 1, 2 and 4, and resistor21 in FIG. 5 having a value of about 10 megohms.

It will be obvious that the above described circuits provide anefiicient and dependable radiation alarm while using negligibleelectrical power in the standby condition. Details of the alarm 15 havenot been shown but it will be understood that besides including astructure which produces a visual or audible signal, the alarm assemblymay include a relay with a holding circuit or a mechanical lock so thatonce tripped the alarm will continue to operate after capacitor 16 hasbeen discharged.

The foregoing disclosure and drawings are merely illustrative of theprinciples of the radiation alarm as disclosed and are not to beinterpreted in a limiting sense. The only limitations are to bedetermined from the scope of the appended claims.

What is claimed is:

1. A radiation alarm for indicating the presence of penetratingradiation above a predetermined value comprising; an ionization chamberhaving an anode and a cathode within a permeable envelope; said chamberarranged to pass current which is proportional to the intensity of thepenetrating radiation incident thereon but passing constant current inresponse to a wide range of applied voltages; a constant current devicein series with the ionization chamber and a source of potential; saidconstant current device including an anode, a cathode,

and a source of constant ionization within an envelope; an electrostaticswitch having a movable switch blade positioned adjacent to a stationaryplate and a switch contact; a connection between the stationary plateand the junction between the ionization chamber and the constant currentdevice; said movable blade connected to the anode of the ionizationchamber in series with a resistor; a gaseous discharge device having ananode, a cold cathode, and a control electrode positioned within anenvelope containing an ionizable gas at reduced pressure; said controlelectrode connected to said switch contact; an alarm connected in seriesbetween the cathode of said discharge device and the negative terminalof the source of potential; and a connection between the anode of saiddischarge device and the positive terminal of the source of potential inseries with a resistor.

2. A radiation alarm as set forth in claim 1 wherein said controlelectrode is connected to the negative terminal of the source ofpotential in series with a resistor.

3. A radiation alarm as set forth in claim 2. wherein said ionizationchamber contains a source of ionizing radiation.

4. An alarm circuit according to claim 2 wherein said constant currentdevice includes two electrodes and is 6 open to the atmosphere, theresistance between said electrodes changing when smoke particles enterthe space between the electrodes.

5. An alarm circuit according to claim 2 wherein said alarm is adjustedto operate when the gaseous discharge is rendered conductive and to benon-operative when the discharge device is not conductive.

References Cited in the file of this patent UNITED STATES PATENTS1,605,911 Banneitz Nov. 9, 1926 1,962,849 Tour June 12, 1934 2,408,051Donelian Sept. 24, 1946 2,702,898 Meili Feb. 22, 1955 2,817,768 ShamosDec. 24, 1957

